An Experiment‐Guided Descriptor Framework for Chain‐Growth CO ₂ Electrocatalysis

The electroreduction of CO 2 to long‐chain hydrocarbons (LCHC) has been recently demonstrated on several transition metal‐based catalysts; yet the catalyst properties enabling this pathway remained unclear. Herein, we combine experiments and modeling to establish mechanistic descriptors to help guide strategies to convert CO 2 to LCHC. We first compare strong *CO‐binding catalysts including Ni, Co, Fe, Ru, Rh, and Pd, and show their different abilities to drive chain‐growth CO 2 electrocatalysis toward LCHC. Hydrocarbon chain growth initiates from *CO formation and hydrogenation to *CH x , followed by successive *CO insertion into a growing *RCH x chain. *CO hydrogenation and *C─*C coupling steps are identified as key kinetic barriers governing chain growth. Guided by these observations, density functional theory calculations establish descriptors rationalizing LCHC formation. Unlike Cu (with moderate *CO binding) that favors *CO dimerization, strong *CO‐binding catalysts favor *CO hydrogenation toward *CH x , thereby opening a route to LCHC. The relative barriers of *CO─*CH x coupling and the competing hydrogen evolution reaction (HER) further modulate LCHC yield. LCHC yield can be experimentally further promoted by 3–7 fold across all catalysts by enhancing *CO hydrogenation. These results establish mechanistic descriptors and provide rational catalyst design principles for LCHC formation.